Home Gateways (HGW) that implement Hybrid Access (HyA) offer clients access to the internet over different access networks, e.g., over a network using DSL and over another network using LTE. In such cases the gateways may be connected to these networks by different interfaces, but they may hide this from the clients.
Being attached to multiple different networks with different configurations causes issues such as discussed by the IETF's working group on Multiple Interfaces (IETF WG MIF), for reference see http://datatracker.ietf.org/wg/mif/charter/. These issues, however, are mainly related to the configuration of the host with multiple interfaces, i.e., the HGW in the above example, due to potentially conflicting configuration information (DHCP, default routes, DNS servers, etc.) received over the different interfaces.
A different, somewhat independent problem occurs in the situation where it is assumed that the DNS servers to be used, i.e. either the same DNS server for all interfaces or a different one per interface, are configured correctly. These DNS servers might resolve a query to different resource records, i.e. different IP addresses, depending on the interface from which the query originated. An example would be the DNS component of a CDN network, which should return content servers that have an advantageous location in relation to the query origin. However, current practices, as described, e.g., in Wasserman, M., Seite, P, RFC 6419: “Current Practices for Multiple-Interface Hosts” (http://datatracker.ietf.org/doc/rfc6419/), typically just query using the default interface, or select and use just one DNS response in case a domain name needs to be resolved. In any case, if the HGW should act as a transparent proxy to clients, only one response should be forwarded to the client in any case.
On the other hand, one of the advantages of being attached to multiple networks is that the capacity of these access connections could be combined (to ‘boost’ the capacity seen by clients). To this end, content should be downloaded over more than one interface at the same time. One method to achieve this is Multipath TCP (MPTCP), but currently there are not many servers implementing and supporting MPTCP. An alternative is downloading content using several (normal) TCP connections, implementing the multipath download on application layer, using e.g. HTTP range requests (for parallel downloads from a single source and from several identical sources, respectively), such as described in K. Evensen et al.: “Using bandwidth aggregation to improve the performance of quality-adaptive streaming”, in Signal Processing: Image Communication, 27(4):312{328, April 2012, or in Pablo Rodriguez and Ernst W. Biersack: “Dynamic parallel access to replicated content in the internet”, in IEEE/ACM Trans. Netw., 10(4):455 {465, August 2002.